This invention relates to single-use hypodermic syringes, and in particular to a single-use hypodermic syringe having a needle assembly which can be changed prior to use of the syringe.
Contagious diseases can be transferred by reusing hypodermic syringes that are intended for single use. The reuse and sharing of such syringes is especially common among intravenous drug users. This places intravenous drug users at high risk for contracting the AIDS virus and encourages the proliferation of drug abuse. Further, the frequent re-use of hypodermic syringes in mass inoculation programs is a problem in certain countries. Such reuse may be responsible for the spread of many diseases in these countries. Additionally, healthcare personnel and other people who handle used syringes are often accidentally stuck with syringes during disposal or destruction thereof.
The problem of hypodermic syringe re-use has been addressed in many ways through the years. One early solution involved destroying the syringe after use. Other solutions involved providing certain methods and devices which the user would employ to destroy or render the syringe inoperable. Unfortunately, these methods and devices are not effective with users who intend to re-use syringes or when the syringe is accidentally mishandled.
A more recent solution has been to provide protective shields that automatically cover the needle of the syringe after use. An example of such a syringe is disclosed in U.S. Pat. No. 5,562,626. The syringe disclose therein is provided with a shield or sheath that automatically extends over and covers the needle of the syringe after the syringe has been used
Although the syringe of U.S. Pat. No. 5,562,626 operates very satisfactorily, it does have a couple of drawbacks. One drawback is that the needle assembly typically employs a small bore needle (25 to 20 gage) which provides for a relatively painless injection. The needle assembly is permanently affixed to the tapered neck of the syringe barrel by an adhesive. This makes it impossible to mount a different needle assembly to the syringe in situations where for example, a large bore needle (18-16 gage) would be desirable to facilitate quick filling of the syringe. Moreover, the needle assembly includes a separately manufactured expansion collar (which forms part of the mechanism which prevents movement of the shield to uncover the needle after use) which undesirably increases the cost of the syringe.
Another drawback of the syringe disclosed in U.S. Pat. No. 5,562,626 is that it incorporates a safety bushing which must to be removed in order to operate the plunger assembly of the syringe. This safety bushing further adds to the cost of the syringe and makes the syringe more complicated to use.
Accordingly, a need exists for a single-use hypodermic syringe which permits changing of the needle assembly, is inexpensive to manufacture, and convenient to operate.
A single-use hypodermic syringe comprises a syringe barrel with distal and proximal ends. The syringe barrel includes a flange at the proximal end thereof and a luer locking collar at the distal end thereof. A needle assembly is removably coupled to the distal end of the syringe barrel. The needle assembly includes a hub and a needle extending from a distal end of the hub. A plunger is telescopically positionable within the barrel. A tubular shield is disposed around the syringe barrel such that the syringe barrel can be moved relative thereto. The shield includes locking prongs extending proximally therefrom, and a spring for moving the syringe barrel from an unused position, where the shield allows exposure of the needle assembly, into a used position where the shield covers the needle assembly. The prongs engage the syringe barrel flange to retain the barrel in the unused position, and disengage from the barrel flange during use of the syringe thereby permitting the spring to move the barrel into the used position.
One aspect of the invention involves providing the needle assembly with an expandable collar (expansion collar) that coacts with the shield to maintain the barrel in the used position. More specifically, the expansion collar expands to engage a locking protrusion provided on the shield protrusion when the barrel is moved to the used position.
Another aspect of the invention involves forming the hub and expansion collar as a single unitary part.
Still another aspect of the invention involves providing the expansion collar with four locking tabs.
A further aspect of the invention involves providing circular hook segments on the prongs for engaging the syringe barrel flange to retain the barrel in the unused position.